[PATCH v18 30/40] libstdc++: Optimize is_pointer trait performance

[Ken Matsui]

This patch optimizes the performance of the is_pointer trait by dispatching to
the new __is_pointer built-in trait.

libstdc++-v3/ChangeLog:

        * include/bits/cpp_type_traits.h (__is_pointer): Use __is_pointer
        built-in trait.
        * include/std/type_traits (is_pointer): Likewise. Optimize its
        implementation.
        (is_pointer_v): Likewise.

Co-authored-by: Jonathan Wakely <jwak...@redhat.com>
Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/bits/cpp_type_traits.h |  8 ++++
 libstdc++-v3/include/std/type_traits        | 44 +++++++++++++++++----
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h 
b/libstdc++-v3/include/bits/cpp_type_traits.h
index 4312f32a4e0..cd5ce45951f 100644
--- a/libstdc++-v3/include/bits/cpp_type_traits.h
+++ b/libstdc++-v3/include/bits/cpp_type_traits.h
@@ -363,6 +363,13 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
   //
   // Pointer types
   //
+#if __has_builtin(__is_pointer)
+  template<typename _Tp>
+    struct __is_pointer : __truth_type<__is_pointer(_Tp)>
+    {
+      enum { __value = __is_pointer(_Tp) };
+    };
+#else
   template<typename _Tp>
     struct __is_pointer
     {
@@ -376,6 +383,7 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
       enum { __value = 1 };
       typedef __true_type __type;
     };
+#endif
 
   //
   // An arithmetic type is an integer type or a floating point type
diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 9c56d15c0b7..3acd843f2f2 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -542,19 +542,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public true_type { };
 #endif
 
-  template<typename>
-    struct __is_pointer_helper
+  /// is_pointer
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
+  template<typename _Tp>
+    struct is_pointer
+    : public __bool_constant<__is_pointer(_Tp)>
+    { };
+#else
+  template<typename _Tp>
+    struct is_pointer
     : public false_type { };
 
   template<typename _Tp>
-    struct __is_pointer_helper<_Tp*>
+    struct is_pointer<_Tp*>
     : public true_type { };
 
-  /// is_pointer
   template<typename _Tp>
-    struct is_pointer
-    : public __is_pointer_helper<__remove_cv_t<_Tp>>::type
-    { };
+    struct is_pointer<_Tp* const>
+    : public true_type { };
+
+  template<typename _Tp>
+    struct is_pointer<_Tp* volatile>
+    : public true_type { };
+
+  template<typename _Tp>
+    struct is_pointer<_Tp* const volatile>
+    : public true_type { };
+#endif
 
   /// is_lvalue_reference
   template<typename>
@@ -3254,8 +3268,22 @@ template <typename _Tp, size_t _Num>
   inline constexpr bool is_array_v<_Tp[_Num]> = true;
 #endif
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
+template <typename _Tp>
+  inline constexpr bool is_pointer_v = __is_pointer(_Tp);
+#else
 template <typename _Tp>
-  inline constexpr bool is_pointer_v = is_pointer<_Tp>::value;
+  inline constexpr bool is_pointer_v = false;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp*> = true;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp* const> = true;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp* volatile> = true;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp* const volatile> = true;
+#endif
+
 template <typename _Tp>
   inline constexpr bool is_lvalue_reference_v = false;
 template <typename _Tp>
-- 
2.42.0